Hypersonic crossflow instability and transition on a circular cone at angle of attack

To investigate the effect of Reynolds number, tunnel noise and surface roughness on the crossflow instability, a 7° half-angle cone was tested at 6° angle of attack with temperature-sensitive paint. All tests were performed in the Boeing/AFOSR Mach-6 Quiet Tunnel. The temperature-sensitive paint was successfully used to qualitatively visualize boundary-layer transition and stationary crossflow vortices. Tunnel noise was found to have a significant effect on the crossflow instability, promoting transition when the tunnel noise was high. Transition was never realized under fully quiet flow. Increasing Reynolds number also proved to have an effect on the crossflow instability. Under quiet flow, an increase in Reynolds number created larger amplitude stationary vortices, while under noisy flow the increase in Reynolds number caused transition to move upstream.;The effect of surface roughness on the crossflow instability was also studied. This surface roughness effect was studied in two ways: by varying the frustum roughness and by varying the nosetip roughness. The frustum roughness was varied by altering the finish of the temperature-sensitive paint. The nosetip roughness was varied by polishing the stainless steel nosetip. For both cases, it was found that the magnitude and the azimuthal variations of the forward-facing step at the nosetip-frustum junction was most likely dominating the formation of the streamwise vorticity. Thus, before the effect of distributed surface roughness can be studied, the forward-facing step needs to be rendered negligible.;Preliminary tests were also performed with the 7° half-angle cone placed at 0° angle of attack in order to validate a procedure for obtaining quantitative heat transfer from temperature-sensitive paint. However, this effort is not yet successful.